• Gather all the ingredients. Here, I show what you'll need to make homemade tsuyu (noodle dipping sauce).

  To prepare a quick dipping sauce instead using bottled mentsuyu (concentrated noodle soup base), see my optional recipe at the end.
  

To Make the Homemade Dipping Sauce (Tsuyu)

• Add ⅔ cup dashi (Japanese soup stock), 2 Tbsp mirin, and 1 tsp sugar to a small saucepan. Bring it to a simmer over medium heat and stir to dissolve.
  
• Next, add 2 Tbsp soy sauce. Bring it back to a simmer, then turn off the heat. Transfer to a heat-resistant container or serving pitcher and set in a bowl of ice to let cool (you can make it ahead and keep in the fridge).
  

To Prepare the Noodles

• Bring a large pot of water to a boil. Add 2 servings udon noodles (frozen; no need to defrost) and boil for 1 minute to heat through. Nami's Tip: I use my favorite frozen Sanuki udon from the Japanese market. Alternatively, Hime Dried Udon is a decent option from Amazon; cook according to package directions.
  
• Drain in a sieve. Thoroughly rinse off the udon's starch under running water until they’re no longer slippery. Once cool, place the noodles in an ice bath to chill for 30–60 seconds (if you chill too long, the noodles become too firm).
  

To Prepare the Condiments

• Cut 1 green onion/scallion into thin slices. Peel and grate ½ inch ginger; I use a ceramic grater. Put sliced green onion, grated ginger, and optional wasabi on individual small plates.
  

To Serve

• Drain the chilled udon noodles well. Divide onto individual serving plates along with a few of the ice cubes. Divide the cooled tsuyu sauce into individual dipping cups. Serve the cold udon noodles and dipping sauce. Add the condiments directly to the dipping sauce and enjoy.
  

To Store

• Store leftover dipping sauce in a clean, airtight container in the refrigerator for up to a week. I recommend cooking the udon noodles just before serving.

(Optional) To Make the Quick Dipping Sauce (4 servings)

• Add ½ cup mentsuyu (concentrated noodle soup base), 1 piece kombu (dried kelp), and ½ cup katsuobushi (dried bonito flakes) to a measuring cup or container. Let it steep for at least 10 minutes or overnight in the fridge. Drain the mentsuyu through a sieve (discard or repurpose the kombu and katsuobushi). To use: Dilute with 1½ cups water, then serve into individual dipping cups.
  
• Nami's Tip: The mentsuyu brand I use is concentrated 3 times for cold noodle dipping sauce (men no tsuketsuyu). The dilution ratio is one part mentsuyu to three parts water (1 : 3). Follow your bottle's dilution instructions, as each brand is different. If you have “straight” mentsuyu, use it as is without diluting.